Atmospheric River moving out, weaker storm systems next week

April 7, 2018 – Scattered showers and possibly a thunderstorm will continue today. Colder and much less wet storm systems are possible Tuesday through next weekend.

Discussion

Advertisement

The main plume of moisture associated with the Atmospheric River has shifted south and east of our forecast area this morning. 2-day precipitation totals are largely on track with previous projections: 1 to 4 inches of rain across the Valley, and 3 to 7 inches over the foothills and mountains. Profiler data suggests snow levels remain above 10000 feet at this hour, although signs point to a rapid lowering of snow levels over the next few hours.

Several reports of localized roadway and small stream flooding have come in during the overnight and morning hours. Additionally, several rock slides have occurred over steep mountain terrain. Water levels will be slow to recede this weekend (and in some locations, will continue to rise), and have issued an Urban and Small Stream Flood Advisory to highlight these concerns.

A few showers will continue today mainly along the Sacramento Valley and adjacent mountains. Short-range models suggest a modest amount of instability across the NE Sac Valley and adjacent foothills this afternoon. As such, we may see a few low-topped thunderstorms today.

We’ll have a few days to dry out before the next storm system arrives on Tuesday. This next one will be considerably weaker, with only light precipitation amounts expected across the region.

Extended discussion (Wednesday through Saturday)

Pacific frontal system moves across Interior NorCal Wed into Thu bringing widespread rain with mountain snow. Snow levels look to be around 4500 to 5500 feet Wed, lowering to 3000 to 4000 feet Thu. Precip amounts attm look generally light with this system, generally below half an inch in the Central Valley, and between a quarter inch to inch in the foothills and mountains. Dry weather returns Friday then unsettled over the weekend.